This recombinant rabbit monoclonal antibody recognizes a protein of 38kDa that is identified as synaptophysin. It is an N-glycosylated integral membrane protein found in neurons and endocrine cells. Synaptophysin contains four transmembrane domains and may function as a gap junction-like channel. This antibody identifies normal neuroendocrine cells and neuroendocrine neoplasms. Diffuse, finely granular, cytoplasmic staining is observed, which probably correlates with the distribution of the antigen within neurosecretory vesicles. Synaptophysin is an independent, broad-range marker of neural and neuroendocrine differentiation.